Lacrimal implants are devices that are inserted into a punctum and an associated lacrimal canaliculus of an eye, either to block drainage of tears (to prevent conditions such as dry eye), or to contain a quantity of drug for release into the eye.
FIGS. 1-2 illustrate example views of anatomical tissue structures associated with an eye 100. Certain of the anatomical tissue structures shown may be suitable for treatment using the various lacrimal implants and methods discussed herein. The eye 100 is a spherical structure including a wall having three layers: an outer sclera 102, a middle choroid layer 104 and an inner retina 106. The sclera 102 includes a tough fibrous coating that protects the inner layers. It is mostly white except for the transparent area at the front, commonly known as the cornea 108, which allows light to enter the eye 100.
The choroid layer 104, situated inside the sclera 102, contains many blood vessels and is modified at the front of the eye 100 as a pigmented iris 110. A biconvex lens 112 is situated just behind the pupil. A chamber 114 behind the lens 112 is filled with vitreous humor, a gelatinous substance. Anterior and posterior chambers 116 are situated between the cornea 108 and iris 110, respectively and filled with aqueous humor. At the back of the eye 100 is the light-detecting retina 106.
The cornea 108 is an optically transparent tissue that conveys images to the back of the eye 100. It includes a vascular tissue to which nutrients and oxygen are supplied via bathing with lacrimal fluid and aqueous humor as well as from blood vessels that line the junction between the cornea 108 and sclera 102. The cornea 108 includes a pathway for the permeation of drugs into the eye 100.
Turing to FIG. 2, other anatomical tissue structures associated with the eye 100 including the lacrimal drainage system, which includes a secretory system 230, a distributive system and an excretory system, are shown. The secretory system 230 comprises secretors that are stimulated by blinking and temperature change due to tear evaporation and reflex secretors that have an efferent parasympathetic nerve supply and secrete tears in response to physical or emotional stimulation. The distributive system includes the eyelids 202 and the tear meniscus around the lid edges of an open eye, which spread tears over the ocular surface by blinking, thus reducing dry areas from developing.
The excretory system of the lacrimal drainage system includes, in order of flow, drainage, the lacrimal puncta, the lacrimal canaliculi, the lacrimal sac 204 and the lacrimal duct 206. From the lacrimal duct 206, tears and other flowable materials drain into a passage of the nasolacrimal system. The lacrimal canaliculi include an upper (superior) lacrimal canaliculus 208 and a lower (inferior) lacrimal canaliculus 210, which respectively terminate in an upper 212 and lower 214 lacrimal punctum. The upper 212 and lower 214 punctum are slightly elevated at the medial end of a lid margin at the junction 216 of the ciliary and lacrimal portions near a conjunctival sac 218. The upper 212 and lower 214 punctum are generally round or slightly ovoid openings surrounded by a connective ring of tissue. Each of puncta 212, 214 leads into a vertical portion 220, 222 of their respective canaliculus before turning more horizontal at a canaliculus curvature 250 to join one another at the entrance of the lacrimal sac 204. The canaliculi 208, 210 are generally tubular in shape and lined by stratified squamous epithelium surrounded by elastic tissue, which permits them to be dilated. As shown, a lacrimal canaliculus ampulla 252 exists near an outer edge of each canaliculus curvature 250.
A variety of challenges face patients and physicians in the area of drug delivery, for example, ocular drug delivery. In particular, the repetitive nature of the therapies (multiple injections, instilling multiple eye drop regimens per day), the associated costs, and the lack of patient compliance may significantly impact the efficacy of the therapies available, leading to reduction in vision and many times blindness.
Patient compliance in taking the medications, for example, instilling the eye drops, can be erratic, and in some cases, patients may not follow the directed treatment regime. Lack of compliance can include, failure to instill the drops, ineffective technique (instilling less than required), excessive use of the drops (leading to systemic side effects), and use of non-prescribed drops or failure to follow the treatment regime requiring multiple types of drops. Many of the medications may require the patient to instill them up to 4 times a day.
A conventional method of drug delivery is by topical drop application to the eye's surface. Topical eye drops, though effective, can be inefficient. For instance, when an eye drop is instilled in an eye, it often overfills the conjunctival sac (i.e., the pocket between the eye and the associated lids) causing a substantial portion of the drop to be lost due to overflow of the lid margin and spillage onto the cheek. In addition, a large portion of the drop remaining on the ocular surface can be washed away into and through a lacrimal canaliculus, thereby diluting the concentration of the drug before it can treat the eye. Further, in some cases, topically applied medications have a peak ocular effect within about two hours, after which additional applications of the medications should be performed to maintain the therapeutic benefit.
To compound ocular management difficulty, subjects often do not use their eye drops as prescribed. Noncompliance rates by drop users of 25% and greater have been previously reported. This poor compliance can be due to, for example, forgetfulness or an initial stinging or burning sensation caused by the eye drop and experience by a subject. Instilling eye drops in one's own eye can be difficult, in part because of the normal reflex to protect the eye. Therefore, one or more drops may miss the eye. Older subjects may have additional problems instilling drops due to arthritis, unsteadiness, and decreased vision. Pediatric and psychiatric populations pose difficulties as well.
One promising approach to ocular drug delivery is to place an implant that releases a drug in tissue in or near the eye. However, providing a sustained release of a particular ophthalmic drug at a therapeutic dose over a desired period of time is challenging. Moreover, use of a lacrimal implant provides a limited volume which to include the drug and a sustained release matrix, wherein elution of the drug must be both relatively constant and at a therapeutic dose over the desired time period.
In light of the above, it would be desirable to provide sustained release of certain ophthalmic drugs that overcome the at least of the above mentioned shortcomings.